A power distribution system is generally made up of a high-voltage system (normally, 6600 V) and a low-voltage system (for example, 100 V to 200 V). Power-receiving terminals used by general consumers are connected to the low-voltage system. Electric utilities are obligated to maintain the voltage at the power-receiving terminals used by general consumers within an appropriate range (for example, maintain the voltage between 95 V and 107 V in the case of a receiving power of 100 V). Therefore, power utilities adjust the amount of control (for example, operate the tap) of a voltage control apparatus (such as an LRT (Load Ratio Control Transformer: on-load tap-changer transformer) or an SVR (Step Voltage Regulator)) connected to the high-voltage system in order to maintain the voltage at the power-receiving terminals used by general consumers. In the following descriptions, the power distribution system indicates a high-voltage system thereof unless otherwise specified.
Conventionally, a local voltage control device is commonly used for voltage control in power distribution systems. The local voltage control device is integrated with or provided along with a transformer-type voltage control apparatus such as an LRT or an SVR, and it controls the voltage of the voltage control apparatus in an autonomous distributed manner on the basis of measurement information (voltage and power flow) near the location point of the voltage control apparatus. As a voltage control apparatus, other than the above transformer-type voltage control apparatuses, reactive-power-controlled voltage control apparatuses are commonly known, such as a phase modifying facility with a function of automatically switching between operating and non-operating (such as a phase advancing capacitor or a shunt reactor), an SVC (Static Var Compensator: static reactive-power compensator), or a PCS (Power Conditioning System: power conditioner) with a reactive-power modifying function. Local voltage control devices that respectively correspond to these voltage control apparatuses are also at the practical stage. The PCS is, for example, a power conditioner for photovoltaic power generation. The PCS connects a photovoltaic power-generation facility or a storage battery to a power distribution system.
These local voltage control devices are configured with the assumption that fluctuations in load distribution in the power distribution system are uniform, that is, the voltage at each point of the power distribution system changes in the same direction over time. However, in recent years, for example, due to diversification in the use of electricity and the widespread use of distributed power supplies due to photovoltaic power generation and the like, the load distribution in the power distribution system tends to fluctuate greatly and non-uniformly over time. This makes it difficult to maintain an appropriate voltage for conventional voltage control in the power distribution system.
Therefore, instead of the voltage control system of the autonomous distribution type, a method has been proposed to provide centralized control of the voltage of the power distribution system in a consistent manner over the entire system (a centralized control method). Specifically, a mechanism has been proposed in which measurement information (voltage and power flow) at multiple points within the power distribution system is collected in a centralized voltage control device by using a dedicated network, this centralized voltage control device determines the amount of control (reactive power or the like) of each voltage control apparatus on the basis of the measurement information, and then the centralized voltage control device automatically and remotely indicates the amount of control to each voltage control apparatus (see, for example, Patent Literature 1).